The present invention relates to an art of buffer control for fairly providing virtual channels in different service classes by a switch on Asynchronous Transfer Mode (ATM) network wherein a plural of service classes are available.
One of conventional data output methods from a plural of buffers by a buffer control unit is a polling method. In this method, data is sequentially taken one by one from each buffer. Another conventional method is Weighted Fair Queuing (James W. Roberts, "Rate Envelope Multiplexing and Rates Sharing in B-ISDN" disclosed in Trans. Commun. Vol. E78-B, No.4 April 1995). In this method, a weighted of service is determined according to how long a packet waits in a queue.
In the conventional output method from a plural of buffers by a buffer control unit, output from a buffer is determined regardless of the number of virtual channels in service classes that are input to each buffer. In the polling method, in case of a switch comprising a buffer in each service class is used, when the number of virtual channel in a service class increased, output from the buffer was less frequent in each virtual channel than in virtual channel in another service class.
In addition, in the Weighted Fair Queuing method, because a weighted of service is determined according to how long a packet waits in a queue, service is more fairly offered than the polling method. However when one virtual channel sent a large burst very quickly, the virtual channel was priorly offered. As a result, virtual channels were not always fairly offered.